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low idle warm 90 jeep 4.0



 
 
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  #1  
Old March 17th 06, 02:32 PM posted to rec.autos.makers.jeep+willys
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Default low idle warm 90 jeep 4.0

Hi Folks:
I have a '90 Cherokee Laredo injected 4.0. When it's warm, after
I've restarted it, it goes through this phase:

If I let it sit and idle, it will slowly go from say 1,000 RPM to 600
or so, and it will be fine. It I step on the gas at all, even if it's
just pulling away from the gas-station pump, it will drop to almost
stalling speed. Once in a while it does stall. Instead, if I let it
idle for about 2 minutes, this doesn't happen. I've changed the O2
sensor, a few of years ago. I've put about 30k miles on it since.
Could that be bad? The last time it STOPPED doing this was one time I
had the gas-tank down to change the pump, which I've done twice so far.
Maybe it's Jersey Gas. This might be something that clears up when I
disconnect-reconnect the battery. I'll have to try that again. Or,
maybe there's a chip upgrade?
Thanks!
Harry

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  #2  
Old March 17th 06, 03:03 PM posted to rec.autos.makers.jeep+willys
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Default low idle warm 90 jeep 4.0

Your symptoms can be caused by a dirty connection on the TPS. I
recommend spray contact cleaner on them to clean them up. WD40 will
work in a pinch.

Our idle goes something like yours every couple years and the clean
fixes it right up.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

HarryHydro wrote:
>
> Hi Folks:
> I have a '90 Cherokee Laredo injected 4.0. When it's warm, after
> I've restarted it, it goes through this phase:
>
> If I let it sit and idle, it will slowly go from say 1,000 RPM to 600
> or so, and it will be fine. It I step on the gas at all, even if it's
> just pulling away from the gas-station pump, it will drop to almost
> stalling speed. Once in a while it does stall. Instead, if I let it
> idle for about 2 minutes, this doesn't happen. I've changed the O2
> sensor, a few of years ago. I've put about 30k miles on it since.
> Could that be bad? The last time it STOPPED doing this was one time I
> had the gas-tank down to change the pump, which I've done twice so far.
> Maybe it's Jersey Gas. This might be something that clears up when I
> disconnect-reconnect the battery. I'll have to try that again. Or,
> maybe there's a chip upgrade?
> Thanks!
> Harry

  #3  
Old March 17th 06, 04:56 PM posted to rec.autos.makers.jeep+willys
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Default low idle warm 90 jeep 4.0

Mike Romain did pass the time by typing:
> Your symptoms can be caused by a dirty connection on the TPS. I
> recommend spray contact cleaner on them to clean them up. WD40 will
> work in a pinch.
>
> Our idle goes something like yours every couple years and the clean
> fixes it right up.


That and probably a gummed up/sticky IAC valve or butterfly. Amazing
what a teeny bit of crud in the wrong place can do.

--
DougW


  #4  
Old March 17th 06, 06:26 PM posted to rec.autos.makers.jeep+willys
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Default low idle warm 90 jeep 4.0

How long has it been since you've cleaned the throttle body? Most
don't ever do it at all. It could be a PCV valve that is damaged and
has dropped the valve portion down into the engine creating a big
vacuum leak, a really dirty throttle body or a bad spot on the TPS.
When you clean out the TB, use a very soft toothbrush and a soft cloth,
along with TB-friendly cleaner, not carb cleaner. Work with the engine
OFF, and take your time cleaning all the gunk off the sides and the
butterfly valve.

While you're in there, pull your EGR valve and give that a good
cleaning as well. Sometimes they get so gunked up that they stick
open, creating a vaccum leak.

Also, on those TPS's, aftermarket units are junk. Buy only an OEM
replacement. Same goes for the EGR valve, if you ever need to swap it
out. I found this all out the hard way.

  #5  
Old March 17th 06, 06:36 PM posted to rec.autos.makers.jeep+willys
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Default low idle warm 90 jeep 4.0

The 4.0 doesn't have an EGR, just a CCV. When it's tube plugs, oil
blows into the air filter.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

JD Adams wrote:
>
> How long has it been since you've cleaned the throttle body? Most
> don't ever do it at all. It could be a PCV valve that is damaged and
> has dropped the valve portion down into the engine creating a big
> vacuum leak, a really dirty throttle body or a bad spot on the TPS.
> When you clean out the TB, use a very soft toothbrush and a soft cloth,
> along with TB-friendly cleaner, not carb cleaner. Work with the engine
> OFF, and take your time cleaning all the gunk off the sides and the
> butterfly valve.
>
> While you're in there, pull your EGR valve and give that a good
> cleaning as well. Sometimes they get so gunked up that they stick
> open, creating a vaccum leak.
>
> Also, on those TPS's, aftermarket units are junk. Buy only an OEM
> replacement. Same goes for the EGR valve, if you ever need to swap it
> out. I found this all out the hard way.

  #6  
Old March 19th 06, 06:12 PM posted to rec.autos.makers.jeep+willys
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Default low idle warm 90 jeep 4.0

Where is the CCV located? I'm not finding it in my book.

~Casper
'93 GC Ltd.

>The 4.0 doesn't have an EGR, just a CCV. When it's tube plugs, oil
>blows into the air filter.
>
>Mike
>86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
>88 Cherokee 235 BFG AT's
>Canadian Off Road Trips Photos: Non members can still view!
>Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
>(More Off Road album links at bottom of the view page)

  #7  
Old March 19th 06, 06:34 PM posted to rec.autos.makers.jeep+willys
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Default low idle warm 90 jeep 4.0

Casper did pass the time by typing:
> Where is the CCV located? I'm not finding it in my book.


http://www.off-road.com/jeep/cheroke...ltr/blowby.htm

Roughly the same for all 4.0 engines.

--
DougW


  #8  
Old March 19th 06, 08:56 PM posted to rec.autos.makers.jeep+willys
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Default low idle warm 90 jeep 4.0

You're right, Mike. No EGR at all on my rig, and it's probably the
same on all 4.0's. No wonder it runs so well. EGR is the
technological equivalance of throwing a wet blanket on a fire, and
they're difficult to clean when they get gummed up. Smog check techs
love 'em though; they're good for retest business.

I'm going to put my money on the TPS and a dirty throttle body. Some
older computers will throw a code for a low TPS signal, but on a '90,
it's doubtful. Another symptom of TPS failure is an automatic
transmission OD that keeps dropping in and out when cruising. One
could hook up a DVM and check it manually, but they're cheap enough
that replacement makes more sense.

Let us know what you find, Harry.

-JD

  #9  
Old March 19th 06, 10:01 PM posted to rec.autos.makers.jeep+willys
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Default low idle warm 90 jeep 4.0

The early 4.0's had EGR's but they dropped them at some point. I know
the 87 - 89 XJ/MJ using the Renix computer had them - I've cleaned
mine a couple of times.

My MJ had real idle problems and curing them was a step by step
process. Cleaning the throttle body made a big difference (don't
forget the MAP sensor port!), cleaning the connectors also helped but
the last little bit of surge/die coming to a stop persisted until I
changed out the O2 sensor. It tested good, but the tail pipe said it
was idling rich (black soot, black smoke accelerating from idle when
hot) so I changed the sensor. Now all I have to do is clean the
connectors every so often.

On Sun, 19 Mar 2006 19:56:57 UTC "JD Adams" >
wrote:

> You're right, Mike. No EGR at all on my rig, and it's probably the
> same on all 4.0's. No wonder it runs so well. EGR is the
> technological equivalance of throwing a wet blanket on a fire, and
> they're difficult to clean when they get gummed up. Smog check techs
> love 'em though; they're good for retest business.
>
> I'm going to put my money on the TPS and a dirty throttle body. Some
> older computers will throw a code for a low TPS signal, but on a '90,
> it's doubtful. Another symptom of TPS failure is an automatic
> transmission OD that keeps dropping in and out when cruising. One
> could hook up a DVM and check it manually, but they're cheap enough
> that replacement makes more sense.
>
> Let us know what you find, Harry.
>
> -JD
>



--
Will Honea
  #10  
Old March 20th 06, 12:18 AM posted to rec.autos.makers.jeep+willys
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Posts: n/a
Default low idle warm 90 jeep 4.0

Hi Guys:
Thanks for the good info. It's been too cold and windy for me today
to do too much, but I did tap into the O2 sensor and that seems pretty
non-responsive. The voltage slowly drops from about .45 to .3 volts,
motor still running and no engine lights. Shouldn't it be closer to
..5V? Even with that, it seems to run fine after its ran a few minutes.
Humm. Maybe that engine light is burnt out. Any quick ways to check
for codes, with a laptop or something?
Thanks!
Harry

 




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